BMR Calculator

Verified 2026-04-30 Report an error

yr
in
lb
Basal metabolic rate
1,690

BMR formulas like Mifflin-St Jeor are population-average predictions with ±10% variation; actual metabolism shifts with genetics, lean mass, and thyroid function. Not medical advice; consult a physician or registered dietitian for weight or medical decisions.

On this page
  1. Overview
  2. Key takeaway
  3. How it's calculated
  4. Quick tricks
  5. Examples
  6. FAQ
  7. Related calculators
  8. Popular tools

A BMR calculator estimates your basal metabolic rate, the calories your body burns at complete rest, just to keep organs running and cells alive. Enter sex, age, height, and weight; the calculator returns a BMR in kcal/day using the Mifflin-St Jeor equation, currently considered the most accurate predictive formula for healthy adults.

Useful as the foundation of any calorie-budgeting plan. BMR plus an activity multiplier gives total daily calorie burn (TDEE), which is what you compare to caloric intake when targeting weight changes. BMR alone is sedentary at-rest energy expenditure.

Three formulas dominate this space. Mifflin-St Jeor (1990, used here) is the most accurate for healthy adults across a normal weight range, validated against indirect calorimetry. Harris-Benedict (1919, revised 1984) tends to overestimate BMR by 5-10% and is progressively being retired. Katch-McArdle uses lean body mass instead of total weight and is the most accurate of the three, but only if you have a recent body-fat measurement (DEXA, BodPod, or callipers). For most people without a body-fat number, Mifflin-St Jeor is the right default. Real BMR varies ±10% from any predictive formula based on genetics, thyroid function, and recent diet history.

Key takeaway

BMR accounts for ~60-75% of total daily calories burned for most sedentary or moderately-active adults. Activity (NEAT, exercise, work) accounts for the rest. This is why "metabolism" matters less than most people assume, most of your daily energy expenditure happens automatically, and the lever you control most easily is activity, not metabolism.

How it's calculated

The Mifflin-St Jeor equation (1990), with metric units:

  • Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
  • Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

This calculator takes pounds and inches and converts internally. The equation was validated against indirect calorimetry (gold-standard metabolic measurement) and is consistently more accurate than the older Harris-Benedict formula, especially for heavier individuals where Harris-Benedict overestimates.

To get TDEE (total daily energy expenditure), multiply BMR by an activity factor:

  • 1.2, sedentary (desk job, no formal exercise)
  • 1.375, lightly active (light exercise 1-3 days/week)
  • 1.55, moderately active (moderate exercise 3-5 days/week)
  • 1.725, very active (hard exercise 6-7 days/week)
  • 1.9, extra active (physical job + hard daily training)

For weight loss, target a 250-500 kcal/day deficit below TDEE; for gain, the same surplus. More aggressive targets backfire, extreme deficits cause muscle loss and metabolic adaptation.

Source: Mifflin-St Jeor (1990), currently considered the most accurate predictive formula for BMR

Examples

  1. 35-year-old man, 5'10", 165 lb

    Basal metabolic rate 1,690

    A 35-year-old man at 5'10"/165 lb has a Mifflin-St Jeor BMR of about 1,690 kcal/day. With a desk job (×1.2 activity factor), TDEE ≈ 2,030 kcal/day. With 4 days/week of moderate exercise (×1.55), TDEE ≈ 2,620 kcal/day. The 590-kcal gap shows how much activity actually moves the daily total.

  2. 45-year-old woman, 5'5", 145 lb

    Basal metabolic rate 1,304

    A 45-year-old woman at 5'5"/145 lb has a BMR of about 1,304 kcal/day. Sedentary TDEE (×1.2) ≈ 1,565 kcal; moderately active (×1.55) ≈ 2,021 kcal. Note that BMR drops slowly with age, by age 65, this same person would have a BMR closer to 1,200 kcal/day, all else equal.

Frequently asked questions

What is BMR and how is it different from TDEE?

BMR (Basal Metabolic Rate) is the calories you'd burn lying in bed all day doing absolutely nothing, just keeping organs running. TDEE (Total Daily Energy Expenditure) is BMR plus all the other ways you burn calories: walking, fidgeting, digesting food, and exercise. TDEE = BMR × activity multiplier (1.2 for sedentary, up to 1.9 for very active). For calorie budgeting, TDEE is the relevant number, BMR is the foundation you build on.

How accurate is the Mifflin-St Jeor formula?

Generally within ±10% of measured BMR for most healthy adults, the most accurate of the common predictive equations (Harris-Benedict, Katch-McArdle, Cunningham). Outliers exist: very muscular individuals (where lean mass rather than total weight matters), people with thyroid disorders, and those with unusual body compositions. For high-precision needs, indirect calorimetry (a clinical metabolic test) measures BMR directly and is more accurate than any formula.

Does my BMR change?

Yes, slowly. Lean mass (muscle) burns more calories at rest than fat mass, so building muscle raises BMR by ~6-10 kcal/lb of added muscle per day. Aging drops BMR by ~1-2% per decade after 30, partly from lean-mass loss. Severe calorie restriction causes "metabolic adaptation", BMR drops by ~10-15% beyond what weight loss alone would predict, which is why crash diets often plateau and rebound. Recovery happens slowly with normalized eating and resistance training.

Can I increase my BMR?

Modestly, yes. Resistance training to build lean mass is the most evidence-backed lever, each pound of muscle adds 6-10 kcal to daily BMR. Eating adequate protein (0.7-1 g per lb of body weight) supports lean mass. Avoid prolonged severe calorie deficits, which trigger metabolic adaptation. "Metabolism boosters" marketed in supplements rarely deliver meaningful, sustained BMR increases, most studies show effects of <50 kcal/day, not enough to matter for body-composition outcomes.

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